Abstract
Abstract. The frequency of life forms in the fossil record is largely determined by the extent to which they were mineralised at the time of their death. In addition to mineral structures, many fossils nonetheless contain detectable amounts of residual water or organic molecules, the analysis of which has become an integral part of current palaeontological research. The methods available for this sort of investigations, though, typically require dissolution or ionisation of the fossil sample or parts thereof, which is an issue with rare taxa and outstanding materials like pathological or type specimens. In such cases, non-destructive techniques could provide a valuable methodological alternative. While Computed Tomography has long been used to study palaeontological specimens, a number of complementary approaches have recently gained ground. These include Magnetic Resonance Imaging (MRI) which had previously been employed to obtain three-dimensional images of pathological belemnites non-invasively on the basis of intrinsic contrast. The present study was undertaken to investigate whether 1H MRI can likewise provide anatomical information about non-pathological belemnites and specimens of other fossil taxa. To this end, three-dimensional MR image series were acquired from intact non-pathological invertebrate, vertebrate and plant fossils. At routine voxel resolutions in the range of several dozens to some hundreds of micrometers, these images reveal a host of anatomical details and thus highlight the potential of MR techniques to effectively complement existing methodological approaches for palaeontological investigations in a wide range of taxa. As for the origin of the MR signal, relaxation and diffusion measurements as well as 1H and 13C MR spectra acquired from a belemnite suggest intracrystalline water or hydroxyl groups, rather than organic residues.
Highlights
When an organism dies, it is usually quickly decomposed but special conditions – namely the presence of biomineralised structures – sometimes allow for part of its morphological or biochemical characteristics to be preserved
Too, were increasingly often found to contain organic matter (Kidwell and Holland, 2002; Behrensmeyer et al, 2000; Briggs, 2003), be it in cephalopod shells (Abelson, 1954; Westbroek et al, 1979), belemnite rostra (Bandel and Spaeth, 1988; Florek et al, 2004), bones (Abelson, 1954; Schweitzer et al, 2005, 2007; Asara et al, 2007), or wood (Boyce et al, 2001; Siurek et al, 2004). Such observations led to the suggestion that part of the organic material detected in fossils might represent the most stable portion of the molecules originally constituting the individual at the time of its death (e.g. Abelson, 1954; Florkin, 1965; Westbroek et al, 1979; Eglinton and Logan, 1991; Engel et al, 1994; Schweitzer et al, 2007), which opened the door for palaeobiochemical investigations (Blumer, 1965; Albrecht and Ourisson, 1971; Niklas and Gensel, 1976; Weiner et al, 1976; Westbroek et al, 1979; Lowenstein, 1981; Ourisson and Nakatani, 1994; Waggoner, 2002; Schweitzer, 2003; Paabo et al, 2004; Asara et al, 2007), provided that the specimens were excavated and stored in a suitable manner
It is further characterised by (1) the apical line, which represents the axis of the rostrum and marks the trajectory of the apex during successive growth stages, (2) composite radial structures formed by crystals radiating out from the apical line to the margin and (3) commarginal growth lines which stem from periodical accretions of radial structures that resulted in spatial variations of the organic content
Summary
It is usually quickly decomposed but special conditions – namely the presence of biomineralised structures – sometimes allow for part of its morphological or biochemical characteristics to be preserved (for reviews, see Behrensmeyer et al, 2000; Briggs, 2003; Durand, 2003; Weiner and Dove, 2003; Middelburg and Meysman, 2007). While a number of techniques exist that can non-destructively image the surface of a specimen (see, e.g., Sælen, 1989; Scott and Collinson, 2003), serial grinding techniques combined with digital photography have long been the only method allowing to reconstruct the three-dimensional structure of fossils at a high spatial resolution (Luo and Eastman, 1995; Luo and Marsh, 1996; Sutton et al, 2001; Siveter et al, 2004; Sutton et al, 2005), yet they trade this achievement for a complete loss of the specimen Due to these technical limitations, obtaining chemical and morphological information from within fossils has generally been mutually exclusive but progress in non-invasive imaging techniques of geomaterials in general has important spill-over effects for palaeontological investigations (Rothwell and Vinegar, 1985; Carlson, 2006). The fossil material figured here is housed at the Museum fur Naturkunde der Humboldt-Universitat zu Berlin, Germany (acronym MB.) and in the Museum fur Natur und Umwelt in Lubeck, Germany (acronym MNU)
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